The present invention relates to a method for bending a glass sheet, wherein a glass sheet is supported on a bending mould in a heating furnace and heated close to a softening temperature by means of a heating field generated by heating element. The invention relates also to an apparatus for bending a glass sheet, said apparatus comprising a heating furnace, a mould for supporting a glass sheet in the heating furnace, as well as an array of heating elements for generating a heating field. The heating elements are typically elongated electric resistance elements, the invention not being limited, however, to the use of such elements only but also other types of heating elements, such as gas burners can be employed.
The prior art methods and equipment, based on gravitational bending of glass, can only be used for bending relatively simple configurations. Complex bending shapes, wherein the bending is effected with a relatively small bending radius and often also about two cross-wise bending axes, have necessarily been bent by embossing between whole-surface moulds. This requires inconvenient and expensive mould technology, wherein a further problem is a contact between mould and glass.
One of the most important qualities in a heating furnace is the proper focusing of heat in terms of both quantity and timing. With the prior art methods and equipment, it is difficult or impossible to achieve the properly proportioned and timed focusing of heat as a result of e.g. the following reasons:
distance between glass and heating resistances is too long PA0 distance between glass and heating resistances cannot be adjusted during a bending operation PA0 mutual distance of heating resistances is too long PA0 parallel heating resistances are not capable of focusing heat on a desired spot PA0 measuring often involves just overall temperature, although a bending process should be controlled on the basis of glass temperature PA0 the heat radiation energy emitted by an individual heating resistance is not correctly dimensioned.